Hydraulic brake



April 26, 193s. L H HUNT 2,115,071

HYDRAULIC BRAKE Filed Feb. 1.6,1935 e sheets-sheet` 1 (f mit Nl 55 i 2 "`l, 1

April 26, 1938. J. H. HUNT 2,115,071

' HYRAULIc BRAKE Filed Feb. 16, 1935 6 Sheets-Sheet 2 .Am-11251938. y HHUNT 2,115,071

HYDRAULIC BRAKE Filed Feb. 16, 1955 6 Sheets-Sheet 3 v gmc/WLM April 26, 1938. ,1. H. HUNT 2,115,071

' HYDRAULIC BRAKE:

Filed Feb. 16. 1955 6 Sheets-Sheet 6 l 656 '11' i i/646 655 645 635 mnu Patented Apr. 26, 1938 PATENT oEEicE HYDRAULIC BRAKE John H. Hunt, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application February 16, 1935, Serial No. 6,768

I'IClaims.

This invention relates to brakes and has been designed as an improvement for use with four wheel hydraulic brakes as used on motor vehicles.

It is known to be desirable that the ratio of braking between the front and rear wheels, taken collectively, shall approximate the ratio of weight supported by the front and rear wheels. It is also known that the weight distribution changes as a vehicle travels on a grade and also that it changes due to inertia incident to deceleration. Even if the weight of a vehicle be divided equally between the frontand rear supporting wheels as it stands at rest or as it travels at a uniform rate on a level road it will be obvious that some of the weight is shifted from the rear wheels to the front wheels when the vehicle travels down hill or is being decelerated.

An object of this invention is to change the ratio of front and rear hydraulic braking forces to correspond with the change in weight distribution.

A further object is to provide means responsive to the change in weight distribution and to deceleration to automatically redistribute the fluid pressure braking forces.

As a still further object the inventor contemplates the resort to servo means through the instrumentality of which the above described automatic redistribution of braking forces may function.

As a still further object in certain forms of the invention unbalanced hydraulic pressures maybe used to effect the shift of braking forces.

Other objects and advantages will appear from the following description.

In the accompanying drawings, Fig. 1 is a schematic plan view of a four wheel hydraulic braking system equipped with my invention.

Fig. 2 is a horizontal section through the double master cylinder unit used with the assem- 2-2 .of Fig. 3.

Fig. 3 is itself a section on line 3-3 of Fig. 2.-

Fig. 4 is a section on line 4-4 of Fig. 3.

Fig. 5 is a section on line 5-5 of Fig. 3.

Fig. 6 is a view in side elevation of a modified form wherein a vacuum servo mechanism is employed as the instrumentality through the aid of which the braking forces are redistributed.

Fig. 7 is a view in elevation and partlyin vertical section of the power unit used in the assembly illustrated in Fig. 6.

Fig. 8 is a detail in end elevation of a part of the operating mechanism shown in Fig. 6.

Fig. 9 shows in side elevation another modification, one wherein hydraulic means is employed for the servo mechanism.

Fig. 10 illustrates mainly in vertical section parts of the operatingmechanism shown in Fig. 9. 5

Fig. 11 shows, for themost part in side elevation, still another embodiment, one wherein the mass of the structure supported by the wheels functions more directly to introduce the servo mechanism to redistribute the braking forces.

Fig. 12 is a view in vertical section of one of the-elements shown by Fig. 11.

Fig. 13 is a view in vertical section of another of the parts shown in Fig. 11.

. Fig. 14 shows in side elevation a modification of 15 the force redistributing device, one wherein in place of the reciprocating piston member of Fig. 5 there is employed a substitute h aving parts of unequal diameters.

Fig. 15 is a section on line l5-I5 of Fig. 14.

Fig. 16 is a longitudinal section on line I6-I6 of Fig. 15.

Fig. 17 is a transverse section through still another form of braking force redistributing device.

Fig. 18 is a side View of the same with the cover removed to illustrate the operating parts, the view being on line I3-l8 of Fig. 17.

Fig. 19 is a section on line l9-I9 of Fig. 1'1.

Figures 1-5 inclusive represent a iirst form in 30 which the invention is shown. Referring to these figures, 2l is used to designate front supporting wheels of a vehicle and 23 marks the rear wheels.

At each wheel is shown a, rotatable brake drum 25 closed by a fixed cover 21. As is conventional in hydraulic brake installations there is secured to the cover 21 and within each drum a so-cailed wheel cylinder operable to expand shoes into drum contact to retard the drum and wheel rotation. No novelty is claimed for the wheel cylinder and no showing of this `element is made. Pipes 29 and 3l extending from the front wheel cylinders are united by a T 33 from winch a pipe 35 is connected by a fitting 31 tothe work end of a front wheel master cylinder 39. Similarly pipes Il and I3 from the rear wheel cylinders are connected to a T 45, the latter connected by a pipe 41 to a fitting 49 at the end of a rear wheel master cylinder 5l. The two master cylinders are constituted by parallel bores in a casting 53. In this casting is a chamber constituting the usual reservoir for the master cylinder. This reservoir is closed by a cover 51. Within the master'cylinders are twin pistonsl 59 operated jointly by rods 6I connected to a cross head 63, the latter '55 connected as by rod 33 tothe lower end of the manually operated pivoted lever or pedal 31. The pistons are thrust to their brake-'release position byv springs 33. As is conventional. small passages 1I anord communication between the reservoir and the master cylinders communicating with the 'latter only inthe brake 'release lpcsitionof the of, piston 1I. From mssterfcylinder 33, the-one communicating with the front wheel brake cylinders, there extends through casting 33 a horisontal conduit 31, the passage closed by a Vplug 33. This horizontal passage or Vconduit 31 extends to a point verticallyabove the bore 13 and a vertical passage 3| unites the passage 31 with the end (right end as seen in Fig. 5) of bore 13. end of bore 13 communicates with master cylinder 3| by means of avertical passage 33, a longitudinal passage 33 anda transverse passage 31 opening Into the cylinder 13 at 33. Within cylinder `13 between the plug 11 andthe piston 1l is a spring I3| normally pressing the piston to the left and into contact wlth-stop'll. The piston 1l has between its ends a notch |33.

To the side wall of casting 33 adjacent the cylinder bore 13 is secured by fastening means I 33 a cover |31. This cover encloses a space I I I within the casing communicating with` the midportion of the cylinder 13. Jcurnaled in cover opening ||3 and in an opening III in the castingisa shaftiil1. varound the shaft'is prevented bya cap ||3 and'packing |2I.- Keyed to the shaft is a lever arm |23. rRotatable on-the end ofk thel shaft is the stem |23 .of a weight or pendulum |21. Fastening means |33 secures together arm |23 and sternl |23. A spring |23' suitably anchored at |33' attached to the stem |23 holds the stem of the weiizht to the right against a stop |3I'. Within the ycover |31 there ispinxed to shaft ||1 an arm |3| fromwhich a pin I3 projects into notch |33.

Ihe operation will be readily understood. When the vehicle is atrest or traveling forward at a uniformrate. pressure Aon pedal 31 pushes both master pistons I3 and forces nuid intothe conduits and wheel cylinders-acting with equal force upon ythe brakes both front and rear. When the brakes are appliedl tothe wheels of a moving vehicle thel load of the supported body tends, under the influencent inertia. to shift forward and more of theload'is then supported by the front wheels than before. If the vvehicle is moving the deceleration resulting from the brakel application tends to cause the weight to swing2 under the influence-of inertia and rock shaft ||1 clockwise (in the illustrative figures).

-This rocking actuallyoceurs and piston 13 is shifted to thek right provided :the inertia is sui'ilycient to overcome spring I 3| which is so .tensioned as to permit the shift to occur upon any appreciable decelerating action. kvThe shift of the piston 13 exerts nuid pressure and supplements the pressure exerted by. the piston of front wheel master cylinder 33 vbecause it is the right' end of cylinder I3 which is-in communication with cylinder 33, Similarly it' relieves the pressure to the left of piston 1l and in the rear wheel brake conduits 41, 43, 4| thus reducing .the pressure on The lefty the rear wheel brakes. In this way as the load is shifted from the rear to the front the braking forces are similarly redistributed.- When deceleration ceases it will be clear that the weight .isv returned to its. position of rest by its springv |23 and the parts are restored to their initial positions. The redistribution will occur evenmore readilyif thebrake is applied whilethe vehicle isv traveling down hill because the action of gravity is available to supplement the influence ofv inertia in swinging the weight and shifting the lpiston 1l. t

It will be possible to use a smaller weight ifl the same is not used to directly shift the. piston 1I but to introduce a source of power which shall serve to shift the piston". `'Ic this end .the vacuum of the engine is available and in Figs. 6,

7, and 8 there is shown a modification to so operate. In this embodiment'the same casting,

I3 may be usedrcontalning theplura'l master cylinders, Vredistributlng cylinder 13 and ycon-` .nected passages. The same pedal 31 is to be used for operating the master pistons and the same conduit system between the master'cylindersand the wheel cylinders. As shown by Fig. 8, itgwill be seen that the lever army |23 isnot connected` to the weight stem |252 the stem in this case carrying a lighter weight |21'. A vacuum powerv cylinder resembling others usedl for vacuum application of brakes is marked 23|.V A pipe 233 connects the closed end of the power cylinder to v the manifold 233 of the engine I231, this being suggested merely as a suitable' source of sfub-` atmospheric pressure. The cylinder has a clo-v sure 239 through the center of which is slidable.

the hub 2|| ci' a piston` designated as a vwhole-by and the closure 209 is seen at223. The hub 2li Suitable packing between the hub 2| I,v

numeral 2|3. This piston includes in addition tofl fthehollow hub 2I| certain discs 2II,.2I1 which` are clamped to the hub2|| by4 a threadedcap has pivoted thereto outside the power cylinder as Y at 223 a rod 221 which latter has a forked end 223 pivoted to armv |23 as shown in Fig. 8.

The hub 2|| has an inner chamber 23| communicating by radial passages 233 with the space at the right side of'the cupped packing 22|. The cap 2|9 has an opening 233 an'ording communication between the chamber`23| and the region. within the power cylinder tothe left of the packing. Spaced from chamber 23| is a second chambers. 'Ihe chamber 231 is adapted to communi-v cate with the atmosphere Iby means of vpassages 24|. Another valve 243 is located coaxiallyl with valve 239. A spring 245 has its ends in engagement with both valves.

249 and a spring 2li engages the hub 2|I and the flange 243. 'I'he reduced extension 233 of 'stem 241 carries slidably the valves 239 and 243.

A nut 2.35 on the Yend of extension 253 normally The two. valves may bev positioned by a stem 241 slidable centrallyl through .the hub 2|I. yThis stem has a flange holds the valvev 243 in brake release position. s

A link 251 is pivotedy to the outer end of stem 241 This link is jointed to the stem I25"at 23|.

valve 243 open whereby Vspring 24! may hold valve 233 on its seat'.

The operation is as follows: Fig. 'I shcwssthe 'rsA 7o It should be explained that spring 23| is stiffer than spring 245 so that it normally holdsy that engine suction prevails on both sides of piston 2| 3 since valve 243 is being held open by spring |.V Admission of aix` to the right of thepiston 2|3 is prevented by the valve 239, thelatter held by spring 245. If now a predetermined extent of deceleration occurs as'the result of brake application, weight |21' swings and pushes link 251 and stern 241 against the resistance of spring 25|. Spring 245 is thus permitted to close valve A243 .and the suction communication between the the right side of the piston 2|3. The unbalanced pressure moves the piston to theleft. Its rod and link connection to the arm |23 functions as before to shift the distributing piston 15. This device is self-closing because the movement of thepiston 2|3 closes valve 239 and cuts off the -air inlet.

The valve may be again opened by the weight if it continues its swing. The extent of redistribution is therefore proportional to the extent of deceleration. v

Figs. 9 and 10 show dlagrammatically a hydraulic servo device for similarly shifting the piston of the redistributing unit. A pump which is a servo pump for this mechanism delivers oil through pipe 303 to a T 305. From the T the oil may flow to an inertia controlled valve device 301 or to a power unit 309. The power unit consists of a cup-shaped cylinder3| I through the bottom of which passes a rod 3|3. A link 3 5 is pivoted to the piston rod and to the arm |23 extending from shaft ||1. 'I'he shaft ||1 extends into the recess of the casting 53 and its rocking motion similarly operates the reciprocating piston 15 of the redistributing device, all as more fully shown in Figs. 1-5 inclusive. The power unit has a cover 3|1 tightly tted and secured thereto as by fastening means 3|9. The piston 32| with its packing 323 is connected to the rod at 325. It is pressed toward the right and into abutment\with a cover boss 321 by a spring 329. The boss has a through aperture 33| for connection with one branch of the T. The boss also has radial apertures 333 affording communication with the right side of the piston. The valve unit 301 comprises a housing 335 shaped as shown and having a cover 331. Pivoted at 339 within the housing is a swinging weight 34| normally held by a spring 343 against the housing wall which thus serves as 'a stop. On .the wall of the housing opposite the stop is a bored out boss 345 to the outer end of which is connected a return pipe 341 leading to the crank case adjacent an oil pump 30|. Slidable within the aperture of boss 345 is a valve 349 having an axial passage 35| communicating by radial passages 353 with the internal chamber 355v of the valve unit 301 when pressed to the right by a spring 351 as shown. 'I'he valve has connected thereto a rod 359 guided as at 35|. 4In an intermediate position the valve rod 359 has a vertically elongated slot 353 through which passes a screw or stud 365 carried by the weight whereby the swinging of the weight about its center 339 reciprocates the valve. When the weight swings clockwise the valve is reciprocated to the left and the radial passages are closed from communication with chamber 355.

In this embodiment of the -invention oil is normally flowing from the pump 30| through the pipe 303 into the valve unit chamber 355, thence through the radial and axial passages of the valve 349 and the return pipe 341 to the crank case.

ance offered by the piston of the power unit At the T it selects this path because of the resist- 5 4backed by the spring 329. If, however, the operator applies the hydraulic brakes by depressing pedal 61 a given decelerating effect causes weight 34| to swing clockwise and cut off the return flow 10 of oil through the valve 349 and pipe 341. In that case the oil enters power unit 309 and pushes the piston 32| against its spring 329. The piston rod operates through link 3|5 to swing arm |23 and reciprocate the piston 15 of the redistributing 15 unit as in the forms of invention previously described.

Figs. v11, 12, and 13 disclose an embodiment of the invention wherein the chassis and body serve the purpose of the swinging weight. In this form 20 of the invention there may be'used the same casting 53 with the master cylinders, redistributing cylinder and connecting passages, and the same rock shaft ||1 with its inner arm |3| and outer arm |23; The chassis frame 40| carries by means 25 of a bracket 403 a control unit 405 located in the vicinity of the rear axle 401. At 409 is shown the, propeller shaft for driving the rear wheels. Within the pump unit 405 is a rock shaft 4| carternal arm 4|5. To the latter is pivoted at 4|1 a link 4|9 the other end of which is pivoted at 42| to some part of the rear axle housing. It will be understood that when brakes are applied to,

-rying an internally disposed, arm 4|3 and an ex- 30 the wheels 401 and their rotation is checked, the 35 inertia of the chassis frame causes the link 4|9 and arm 4|5 to tend to straighten out toward alignment with a resulting clockwise rocking of shaft 4|| with its internal arm 4|3. Within the control unit is an internal cylinder 423 much like the master cylinder of a conventional hydraulic brake system. The chamber 425 within the unit 405 and outside the cylinder 423 is analogous to the reservoir associated with the master. cylinder of the conventional hydraulic brake system. 4.,

hollow ring,44| lxedly located in the piston. At 5 the discharge end of the cylinder is an outlet 443 normally closed against discharge of liquid' by a ball valve 445 pressed by a spring 441 having a suitable abutment. Coaxial with the discharge outlet 443 from the cylinder is a discharge outlet lfrom the valve unit as at 449 to whichis connected a hydraulic conduit 45|. Conduit 45| connects to a power unit designated generally as 453. It comprises a cup-shaped cylinder 455 through the bottom of which slides a rod 451.

The rod is jointed at 459 to arm |23. The conduit 45| communicates through an aperture in head 45| of cylinder 455 with the chamber of the latter to the right of piston 453, the latter secured to rod 451 and carrying packing 455. A 7u spring 491 in abutment with the piston 493 and seated in a recess 461 of the cylinder 455 holds a boss 469 'of the piston against the head 45| which therefore limits the movement of the piston to the right. The power unit 453 may be semeans 413.

also within the control una us is a nains m having a seat y411 for a ball valve 433v held by a spring 413 to prevent passage of liquid from space outwardly of valve 445 and into the .reservoir chamber 425 through radial lpassages 43|. A plunger 433 is reciprocable within a, bored out passage in ntting 415. 'Ihe plungerfengagesfby means ofits reduced stem 435, the ballvalve 430 axfd may be depressed to holdpthat valve oi! its seat land against the pressure of valve-closing spring 413 as shown in Fig. 1,2. Depressionrof the plunger is effected by a bell vcrank 431 engagingthe plunger and pivoted vexternally to the unit at 433. 'Ihe bell crankis rocked counterclcckwiseto depress the plunger by a link 43| pivoted thereto and tothe pedal" beneath its pivot so that the release motion of the pedal ,underv the influence of its conventional spring rocks the bell crank and opens ,valve 433. Depression Yofthe pedal when applying the brake causes the bell crank to move from the plungerwhereupon spring 413 closes the valve 433. Within the power cylinder 455 to the left of the piston 433 is an air vent 433. f

In this form of the invention the parts are in the positions shown when the vehicle is atv resi or traveling at a uniform speed. If the pedal is depressed and wheel rotation retarded, the inertia of the chassis (and its supported body, of course) soon causes a clockwise rotation of rock shaft 4i I and arm 413. Simultaneously with the depression of the pedal valve 433 'has 'closed as explained. The arm 4I3 pushes piston 421to the left. ABuilt up pressure within the cylinder supplements spring 433 in holding valve 431 closed. The piston movement therefore overcomes spring 441 and opens valve 445, thus `delivering iiuid through pipe line 45| to the power unit V453. Movement of lpiston 433 and its rod 45.1 rocks the arm |23 Vand redistributes the fluid pressure as before described. When the pedal is released valve 430 opens and duid under pressure in the power unit 453 Vand,l pipe line 45| is free to iiow into the reservoir as the piston ofthe power unit is being returned by its spring 451. Also, the

return `movement of piston 421 innuenced by its spring 423 creates a void in cylinder 423 which is filled fromy the reservoir by way of the valve 431 opening against the resistance of spring 433.

It is not necessary to use power servo mechanism of the vacuum and hydraulic booster type such as have been described and through which the inertia device is to function. There'is shown in Figs. 14, 15, and 16 an embodiment where the iluid pressure itself developed bythe application of the brakes may be used to effect the braking redistribution in accordance with load redistribution influenced by deceleration. In these` sures numeral 55| is applied to a modincation of casti ing53'of Figs. 1,-5.' This casting is designed for carrying the same master cylinders vas before `and these Vare not illustrated. 'I'he cylinder 13 and redistributing piston of Fig. 5 are changed. Taking the place of cylinder 13 of Fig. 5 is a two diameter recess, numeral 503 being used to designate the cylinder of larger diameter and 53| the aligned and communicating cylinder of lesser di-y ameter. vWithin large cylinder 503 reclprocates a piston 551 and a connected smaller diameter piston 533 reciprocates within cylinder 535, kthe pistons having packings 5H and 5i 3 respectively. Aspring 5I5 in abutment with a plug 511 at the end of the small cylinder pushes the double piscylinder.

on a plug 521 atthat end. At 523 is seen the end of a tubular passageinto the end of the large case of Figs. 1-5) with the mastervcyiinder for the rear brakes. Similarly la passage kmark/ed aords communication between the end of the small cylinder and the master cylinder for the front brakes. Apassagel21 auords communication between the reservoir 523' for the master cylinders and the end oi' thelarge cylinder,l adjacent the junction of the two cylinders.y This permits now of fluid medium in either direction whereby no built up pressure or development of suction at kthe inner end of the large cylinder will irlitrfere with the reciprocation of the combined p s ons. f

,The casting 53| is formed with a recess 523v along the front wall 553 of a slot 530 cut into theV face of. piston 501. 'Ihe path of movement of roller 543 is shown by. dotted lines in Fig. 16. From this figure it will be seen that any fluid pressure acting against piston |51 and tending to move it to the right lis ineifective because it acts substantially axiallyv through the link |41, to rock shaft 535. On the other hand, if shaft 535 is rocked by the swinging of the inertia weight. the roller 543 tendsV to leave the face 553 and if there should be unbalanced fluid pressures on the ends of the composite piston the two pistons may be moved tothe right against the action of spring 5I5 and thereby eifect redistribution ofthe iiuid This corresponds with the passage marked 33 in Fig. 5 and communicates (as in the derstood. When the vehicle is at rest or moving forward at a uniform rate of travel, the parts are as shown in Figs. 14, 15, and 16. If the pedal is depressed pressure is applied uponthe hydraulic wheel brake units as usual. 'I'he fluid pressure of the rear wheel system is effective through passage 523 upon the large diameter end 531 of the composite piston. The fluid pressure ofthe front wheel system is effective through passage 525 upon vthe small diameter end 533 of the composite piston. Owing to the dierence in area the combined piston tends to move to the right -but the eifective force diil'erential is only potential because of the resistance to theV axial push as explained above. Y However, as soon as sumcient deceleration occurs the weight 54| swings clockwise and the roller 543 moves from the slot face 553, whereupon the unbalanced iluid pressure shifts the combined pistons and redistributes they iiuid pressures upon the brakes at the two ends oi" the vehicles as before explained, the extent of redistribution being measured by the extent of swinging of the weight and therefore in proportion to the rate 'ofthe deceleration. Obviously the limit is attained when the product of pressures and areas at the two endsare alike. Upon` release of the pedal the springs 5I5v and .343 restore the parts to their initial positions.

There is still another embodiment shown by Figs 17, 18, and 19 in which a iluid pressure dif-l ferential is employed.- In these figures an inertia weight serves to control a valve, th-rpositionof which renders the potential energy against the large piston available to shift the combined piston assembly when the weight moves under the influence of inertia. vIn these ilgures 60| is used to designate the casting formed as before with the master cylinder, not shown, and with a. two diameter cylinder, the parts 'of which are marked 663 and 666. In this form passages like 623 and 625 of Fig. 16 are used and are similarly marked. Plug 62| with its limiting stop y5|9 is also used in this form but the opposite end opening and plug 6H are omitted. The reservoir is marked by numeral 601. The large diameter piston 669 has an integral (or attached) reduced extension 6|| threaded at its end into the smaller piston 6|3. ,The connecting extension 6|| is axially bored at 626 and has radial passages adjacent the two pistons. A passage 6|5 affords communication between the reservoir 601 and the large diameter cylinder opening into the latter just at the right of the large piston when the latter contacts the stop |3. The extension 6|| has another and intermediate radial passage 6I1 leading from the axial passages. i

Slidable along extension 6|| and fitting both the extension and the wall of the cylinder 603 is a valve 6|9. It has a through passage 62| to effect equalized pressure at its two ends. Between its ends it has an inner recess 623 from which extends a radial passage 625. The casting has a recess 621 extending downwardly from the reservoir to the midportion of the extension 6|| and its slidable valve. Under a cover 629 secured by fastening means 63| over the recess there is a swinging weight 633 pivoted cn a stud 635 threaded into the casting. 'Above the pivot the weight spindle carries a pin 635' projecting into a slot or notch 631 formed in the valve 6| 9. A spring 639 wound around the pivot 635 is anchored at one end 64| to the stem of the weight 633.- The other end is secured to an adjusting screw 643 which may be threaded into the casting to a. variable extent to give the desired spring tension tending to hold the weight against the wall of the casting as shown. The adjusting screw may be covered by a cap 645. A light spring 650 functions to restore the combined piston to the position shown.

In this form of the invention the parts are in the positions shown when the vehicle is at rest or traveling forward at a uniform rate. If, now, the

pedal is depressed and iluid pressure applied to the several wheel brake cylinders, equal pressures develop at the left end of large piston 609 through passage 523 communicating with the rear wheel master cylinder and at the right-end of the small piston 6|3 because of passage 525 communicating with the master cylinder from the front wheel brakes. These equal pressures applied against unequal surfaces tend to shift the combined piston assembly to the right. Such shifting is possible for a slight movement, i. e. until the large piston covers passage 6I5. Further movement is checked because there is no outlet for the escape of iiuid to permit a reduction in capacity of the chamber occupied by the large piston. Quickly, however, the inertia of the pivotaliy mounted weight causes it to shift to the left, Fig. 18. This slides the valve so that the recess 623 registers with radial passage 6H, permitting the escape of uld from large cylinder whereby the unbalanced pressure on the two pistons will effect the piston movement. This, as will be seen, tends to close the registration of 6 23 with 6|1 but the further swinging of the weight reopens the escape. The action will vary in extent inproportion to the extent of deceleration, or until the greater pressure in the small cylinder balances the smaller pressure in the larger cylinder. When the weight and valve return to their position of rest, the pressure head from the reservoir being more eifective on the large piston than on the smallpiston, returns the combined piston to the position shown, this movement being aided by the spring 656.

I claim:

L1. A system of hydraulic brakes for vehicles having iront and rear brakes comprising hydraulic means for jointly applying said brakes in a predetermined ratio, movable means ln iluidcontact with and subject to the pressures of the hydraulic medium acting on said front and rear brakes and adapted to be moved in response to vehicle deceleration to modify said braking ratio.

2. A system of hydraulic brakes for vehicles having front and rear brakes comprising hydraulic means for jointly applying said brakes with pressures equal for both rear brakes and front brakes, movable means engaged by the iluid medium for operating said front brakes and also by the fluid medium for operating said rear brakes, and inertia responsive mechanism operatively connected to said movable means whereby said movable -means may move and change the ratio of braking between the front brakes and rear brakes.

3."`In Abrake mechanism for vehicles having front and rear brakes, means to apply said brakes with equal forces through the instrumentality of movable columns of a liquid medium, a conduit connecting said columns, a member movable in said conduit to change the ratio of forces applied by said columns, said movable member being movable in response to vehicle deceleration.

4. In a hydraulic brake system for vehicles having front and rear brakes, a plurality of master cylinders, a conduit system from a rst one of said master cylinders for said front end brakes, a conduit from the second of said master cylinders for said rear end brakes, a redistributing cylinder, a reciprocable piston therein, conduits connecting the two master cylinders with the ends of said redistributing cylinder and means including an inertia member to shift said reciprocable plston'whereby the front and rear brake pressures may Vary in ratio under the inuence of vehicle deceleration.

5. The invention dei-ined by claim 4, said means including a power servo device acting in response to said inertia member to shift said reciprocable piston.

6. The invention dened by claim 4, said means including a vacuum servo device including a power unit and a valve, the latter controlled by said inertia member whereby the device acts in response to movements of the inertia member to shift said reciprocable piston.

'7. In hydraulic brakes for vehicles having front and rear brakes, a plurality of liquid column brake applying means, one column operable for applying said brakes at one end of the vehicle, the other for applying said brakes at the other end of the vehicle, means acting through the instrumentality of said columns to apply said front brakes and said rear brakes in a predetermined ratio, inertia responsive means movable under the influence of deceleration, and iluid pressure bythe latter may be moved'to supplement the pressure on the front brakes under the innuence of deceleration. v f

9. InV a hydraulic brake system for vehicles having achassis frame and front and rear brakes,

iiuid pressure means to apply-the rear brakes, iiuid pressure means to apply the iront brakes, a common operating means for both. said uid pressure means, conduit connecting said two duid ressure means, movable means. in said conduit.

` other means acting in response to deceleration fluid pressure on the rear wheel brakes, said other t oi' the vehicle incident to the application of said brakes, said other means being operatively connected to said movable means whereby the ratio of said iront and rear braking may be changed.

10. In a hydraulic brake system for vehiclesl having a chassis frameand iront and rear brakes, iiuid pressure meansto apply the rear brakes, fluid -pressure means to apply the yiront brakes. a common operating means for both said iluid pressure means, and other means innuenced by the inertia ci said frame incident to the application of said brakes to supplement the iluid pressure on lsaid iront wheel brakes and reduce the means including a master cylinder, a work cylinder, and a iluid column connecting said cylinders.

1l. In a hydraulic brake system for vehicles having front and rear brakes, iluid pressure means-,to apply said rear brakes, fluid pressure means to apply said front brakes, unitary manually operated means jointly to apply said brakes through the instrumentality of said iluid pressure means, mechanism rresponsive to said iluld pressure and potentially operable to modify the ratio of braking pressures at the front and rear brakes and inertia responsive means to render said potentially operable mechanism active.

ism inmate 'dennen wenn n,- ma coaxial cylinders having unequal diameters, connected pistons one in each cylinder, a conduit to transmit iluid tothe Ircnt brake system `from the smaller cylinder, anda conduitto transmit iiuid to the larger cylinder i'rom the rear brake system.v

13. The invention deiined by claim l1, said mechanism comprising coaxial cylinders having unequal diameters. connected pistons one in each cylinder, a conduit to transmit fluid to the iront brake system'irom the smaller cylinder, a conduit to transmit iiuid to thelarger cyli der lromthe rear brake system. said inertia res nsive means comprising a weight, means positi by said weight to hold said pistons agai i;l movement under unbalanced duid pressures, t e movement of said' weight under the influence of deceleration operable to release said holding means.

14. In a hydraulic brake system for vehicles having iront and rear brakes, fluid pressure means to apply rear wheel brakes, iluid pressure means to apply iront wheel brakes, a two diameter cylinder having its large and small bores connected to said rear andiront brakes respectively, a piston in each cylinder, means in saidy large cylinder connectingsaid pistons and oonstructed to vent the space -between the pistons. valve means to close said vent, and inertia responsive means to move s aid valve and open said vent.

15.7A system oi hydraulic brakes for vehicles having iront and rear brakes comprising a '..iaster cylinder for the iront wheel brakes. a master cylinder for the rear wheel brakes, piston means in `each oi' said cylinders, common means i'or moving said pistons and nuid redistributingmeans having fluid conduit 'connection with both cylinders and inertia-responsive means to actuate said redistributing means whereby the ratio changed.

16. The invention denned by claim l5, said redistributing means` comprising a cylinder, a piston therein, said inertia-responsive means being operably-connected to said piston.

17. In brake mechanism for vehicles having liquid column means for applying iront brakes and liquid column means for applying rear brakes, a conduit connecting said columns, a member movable in said conduit, said movable means adapted to move in response to vehicle deceleration whereby the ratio of front and rear brakes may be changed. v

JOHN H. HUN'r.

of braking at the front and rear of the vehicle is 10 l 

